Author Topic: Electronic stabilization systems. aircraft el al! Link Trainer.  (Read 1176 times)

Online John Hill

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We all know what a Link Trainer is (was?)  https://en.wikipedia.org/wiki/Link_Trainer

The Link is a closed cockpit pilot trainer consisting of a simulation of a single seat aircraft mounted on a stand with movements in yaw, roll and pitch.  The student is under a hood and must guide his aircraft according to instruments and seat-of-pants.

We have one in our museum which is somewhat sacrosanct but we might make another for visitors to the museum to have a go in.

Making the plywood 'plane is no challenge and the mechanical movements should be easy enough.

Our project will require a closed loop system....  pilot inputs-aircraft movement-instrument indications-pilot input.    So, stick forward, 'craft pitches forward, speed indication increases, control sensitivity changes accordingly, instruments do their thing,  RPMs indicate, noise changes...... and so on.

Most of that is software (we we can manage) but tracking the attitude of the 'craft could be a pain involving all manner of electro mechanical do-dads and tangles of wires.

Now the gutz of the issue is how to practically sense 'craft attitude and model air aircraft gyros come to mind.  Comments regards the gyro systems available would be appreciated. :wave:

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Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #1 on: May 12, 2022, 09:34:30 PM »
Wish I could help -- I have a ton of RC model building and flying experience, but I've avoided gyros, because I love the skills required to fly without them. I also flew UL back in my Florida days.

I do have a drone quadcopter with gyros up the wazoo, but that's strictly a commercial black box robot videographer as far as I'm concerned. I have no idea what's inside, and don't care. It's totally boring to me as an RC aircraft, just useful for doing video. I do have a FAA commercial drone pilots license.

However, I would think there are commercial fight simulator programs with inputs and outputs -- and I'm not quite understanding the need for gyros anyway -- but maybe I'm not imagining this right. What about CNC scales on three axes, anyway -- wouldn't they give you attitude feedback?
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #2 on: May 12, 2022, 10:12:19 PM »
Thanks and you may have the very information I am seeking!

I am not thinking of building a flying model and we do know a little about simulators having built one for our museum.

The general idea is that the project will be an enclosed cabin mounted for movement in pitch, yaw and roll.  That in itself does not seem too complicated to connect the 'stick' and rudder to the actuator machinery.

What I am looking for is a way to read the actual attitude of the cabin so as to adjust the instruments, sound effects and vibration in a realistic manner.  That is what I am thinking an electronic gyro unit might provide.

I suspect the outputs of the gyro are correction signals for the three axis,  is that right?   Is the nature of the outputs the same as used to drive model aircraft servos?  If so, for example if my controller program receives an 'up elevator' signal it could change the instruments and sound effects etc to reflect a nose down attitude.  Bear in mind that the movement of the cabin is controlled by the 'pilot' and this gyro system is used only to enhance the environment, instruments, noise, vibration.

I have no doubt there are commercially available systems including entire simulators and yes scales on the machine would be possible.  However this is 'Madmodders' site and does our culture not require us to use our initiative and, for example, modify and use stuff in ways the makers never imagined? :coffee:


One little gyro chip unit must be easier that physical sensors and connecting wires on the 'machine'?


Thanks
John   :beer:
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Offline PekkaNF

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #3 on: May 13, 2022, 01:11:38 AM »
I know one guy who build autopilot to sailboat. He used a cheap gyro/accelerometer card. It provided three axis attitude and rate information out in relatively easy to decode serial communication. I think he used standard arduino platform. Anyway his take was that cheapest ebay module was not good enough, specially on accelerometers, but next step up was allready dood enough. He was struggling a little with serial communication, because it was something like I2C and they are not ment for 7 metre distances. Needed misuse of cat6 cable and I think differential buffers. Can't remeber exactly, I was busy and he explains everything really fast. I could ask the card info if you are interested.

Accelerometers/gyros in consumer grade are cheap now because they are used cellphones, gamecontrollers etc.

Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #4 on: May 13, 2022, 01:16:31 AM »
Yes please, I would like the card info.

John
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Offline PekkaNF

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #5 on: May 13, 2022, 03:36:01 AM »
He said "MPU9250"

One die houses the 3-Axis gyroscope and the 3-Axis accelerometer. The other die houses the AK8963 3-Axis magnetometer from Asahi Kasei Microdevices Corporation. Hence, the MPU-9250 is a 9-axis MotionTracking device that combines a 3-axis gyroscope, 3-axis accelerometer, 3-axis magnetometer and a Digital Motion Processorô (DMP)

Apparently there are Arduino compatible cards for this chip.

PS: He said that it is a chore to calibrate and set this one up. Apparently Murata has a product that gives angle and rate information out with a less hassle....but didn't have the magnetometer (apparently a good idea with an autopilot).
« Last Edit: May 13, 2022, 04:16:12 AM by PekkaNF »

Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #6 on: May 13, 2022, 04:36:46 AM »
Thank you!  I think that is exactly what I am looking for!

John
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Offline PekkaNF

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #7 on: May 13, 2022, 05:43:29 AM »
Update.....He said that you should have a look on this one.
https://www.murata.com/en-eu/news/sensor/gyro/2021/0209

Comes readily axis calibrated. What I gather - after filtering all four leter words - that precalibration of axis would be a REALLY nice thing. Not like calibration of ONE axis will demand to calibrate 6-9 other parameteres and because they are not calibrated you start first with most important parameters and then zone into parameters that have lower coefficiences....and recursion goes on. You develop new hobby out of it pretty fast.


Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #8 on: May 13, 2022, 11:57:02 AM »
Well, of course I'm still back at the CNC scale stage in thinking. Actually, rotary quadrature encoders would probably be more suitable, since you are just rotating on 3 axes. They are cheap on Ebay, and readily interfaced with an Arduino. Programming is straightforward and well documented. You really don't need gyros and calibration and complex dedicated cards to do this, as far as I can see.

The reason RC uses gyros is that the plane  or copter is unconnected to anything mechanically. It's moving through space, and needs onboard stabilization. But in your case the trainer is mechanically controlled and restrained. Would you use a gyro on a mill or lathe for CNC feedback?

https://www.ebay.com/itm/125254761523?hash=item1d29c3fc33:g:K8YAAOSwZbVcCOel

12 bucks, plus shipping......
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #9 on: May 13, 2022, 12:14:16 PM »
Simple can be best if it works!

I had a friend who wanted to create a stabilised model helicopter more years ago than I care to remember, and he wanted a sensor (just a make contact) that would tell him if tilted forwards / backwards / left or right beyond a limit.

I machined a plastic lump with a shallow dish in it with four pairs of contact pins with a ball bearing siting in the bowl such that pairs of pins shorted together when it was tilted in the appropriate direction.

Amazingly it worked quite well on the bench - how reliable it would have been in real life I'm not sure as the ball and pins would no doubt oxidise. I suggested a pool of mercury and a dome cover to seal it, but I don't think he took it any further his interest taking him elsewhere.

Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #10 on: May 13, 2022, 02:01:29 PM »
There are many ways of implementing this kind of functionality and it depends a lot from mechanics how easy it is to get representative indication of attitude straight from the mechanics (or even from actuators). I know one application that went trough the whole cycle from cascaded servo control AND final position measurement to very rigid structure and using only measurements from servo to it's latest iteration of advanced servo and separate from feedback loop magnetic encoder distance measurement again. It all boiled down to a how rigid the structure is in relation to accuracy demand and how economical it is to make different systems to communicate with each others. Programming and interfaces are easily more expensive than transducers in low volume products.

Interfaces/signaling and programming is something that needs good though.

I do agree in principle on Steve's comment on using transducers. That would be in principle very straightforward engineering solution on gimbal system or when there is a rigid mechanics.....From contents I gathered that some thin wall steel (furniture) pipe and plywood might be involved.....that leads easily thoughts on flex/jerk and other inperfections in linkage and then measuring the attitude/acceleration of the platform might be actually most elegant solution after all.

I have no idea if a game controller could be hacked and used as a proof on concept. These simulators are foreign to me.
« Last Edit: May 13, 2022, 04:56:46 PM by PekkaNF »

Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #11 on: May 13, 2022, 02:17:28 PM »
I assume it will be rigid enough not to upset people, and plywood doesn't mean inordinate flexibility, simply depends on design. All kinds of rigid structures are designed in plywood. Including many famous aircraft, which in fact will be the kind of vehicle modeled. DeHavilland Mosquito and Spruce Goose are notable all ply examples, then there were PT boats, and more recently famous IOR racing boats like Golden Dazy, racing iceboats like the DN class, etc, etc..

You can smooth inputs in software as well as choosing an appropriate line rate encoder for the reasonable rate and extension movements needed. I don't think the museum will be simulating crashes or real speeds! The information fineness and rate are going to be very reasonable. There's really no inherent problem in using scales and encoders. I can think of plenty of difficulties in using model type gyros though.  Hey a guy has already gone through this, right? And is still not there.

You will definitely need failsafe software in either case to limit movement rates, and have a safe automatic shutdown routines if sensors provide out of norm expected results, or fail. Movement rates and extents will need to be very limited, etc. But I'm sure you know all of this.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #12 on: May 13, 2022, 02:44:37 PM »
The real thing:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #13 on: May 13, 2022, 04:10:08 PM »
All this interest in my scheme is very gratifying indeed!

PekkaNF The alternative gyro devices are very interesting although I will not make a meal of detailed research just yet, not until I have mentally come to grips with the first suggested device. 

I take your point about deriving position from actuator signals (open or closed loop) but that does usually introduce the need to read absolute positioning at start up, depending on the type of actuator of course.

vtsteam, I have spent a few bux on those encoder devices already and they sure make construction of an anemometer a real breez but of course one must use an absolute one for direction and incremental for the speed, or at least that's the way I do it.


The attraction I see for a gyro (or like device) is that one little device can provide all the attitude information without the concern of running wires hither and yon and slip rings. 


awemawson, I like the plastic dish and ball bearing idea and I am almost tempted to include one somewhere even if only for show!


Well yes, plywood, steel and recycled bed sheets will all be included in the build.   There will also be a F&P washing machine motor, a drive shaft complete with Hook's joint from the junk yard and various curiously clever devices from the John Deere wrecker. Plus I now know why I have been storing a radar rotator from a ship's masthead all these years. 

I assume that is Mr Link's patent drawing?  What a wonder grew from simple beginnings!

Thanks for your interest, information and suggestions.
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Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #14 on: May 13, 2022, 06:17:25 PM »
The attraction I see for a gyro (or like device) is that one little device can provide all the attitude information without the concern of running wires hither and yon and slip rings. 

Heh, I just completed a DRO over bluetooth project. accomodates scales with absolute positioning also quadrature inputs, and even has battery backup for scale positions if the power goes out.

CNC doesn't use slip rings, but also wouldn't the encoders be at the gimbals and not in the trainer body?

Bluetooth serial xmitters HC-05 or HC-06 are like $5

There's an open source firmware sketch for Arduino for the above DRO project here:
http://rysium.com/projects/196-arduino-dro
and construction:
https://www.yuriystoys.com/p/arduino-basic-dro-controller.html

I don't know what the UK rules are re. model aircraft frequency telemetry of gyro data for an alternate use.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #15 on: May 13, 2022, 07:31:55 PM »
Well I had a bit of a think and realize I am looking for the wrong thing! :scratch:

On reflection, I do not need to know where the 'craft is,  I just need to know where it should be! :coffee:

Revised plan:   'Pilot' manipulates controls and this is interpreted by Flight Simulator software in the conventional way which updates the instrument panel and sends position/attitude data to my processor which will move the 'craft as required.   

Is that not a better plan?   Of course I now need to find out how to get data from the flight sim software. :scratch:
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Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #16 on: May 13, 2022, 08:38:13 PM »
Is that not a better plan?   Of course I now need to find out how to get data from the flight sim software. :scratch:

Yes!

Ya know, I was thinking that after the first post but got kind of confused by the gyro talk. But yes.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #17 on: May 13, 2022, 08:42:45 PM »
I would start with FlightGear --it's open source and free. Contact user base/fora and ask questions.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #18 on: May 13, 2022, 09:02:29 PM »
Well I had a bit of a think and realize I am looking for the wrong thing! :scratch:

On reflection, I do not need to know where the 'craft is,  I just need to know where it should be! :coffee:

Revised plan:   'Pilot' manipulates controls and this is interpreted by Flight Simulator software in the conventional way which updates the instrument panel and sends position/attitude data to my processor which will move the 'craft as required.   

Is that not a better plan?   Of course I now need to find out how to get data from the flight sim software. :scratch:


Well the simplest scenario is you use the guts of a 2 pot commercial joystick for the stick (elevator and aileron) and rig another potentiometer for the pedals (rudder) which the flight sim interprets, but also your movement computer interprets the same potentiometers through an onboard A/D converter. Then the flight sim doesn't have to communicate anything. Your computer senses stick position. (well pots are old school, you could substitute encoders, I'm sure with modern simulators. But pots are simple and easy, and widely available as gimbaled joysticks)

There are also available joysticks that can give sensory feedback from a flight simulator: https://wiki.flightgear.org/Force_feedback  .Not sure what other developments there are these days.

Honestly, the feel and timing will never be totally realistic because you can't simulate G forces in turns, etc. For instance, coordinated turns in real life are neutral compared to slip and skid, and they feel different in the seat of the pants. Which is where the expression flying by the seat of your pants comes from. Same thing for acceleration when increasing throttle, or the feel of a dive, etc.

Also the effects of positive, neutral, and negative stability will vary from current stick position. If you model a plane with lots of positive stability, its simulated attitude will most closely align with stick position in timing. You could program into your movement computer a delay after stick movement to align better. If you only modeled one plane, I bet you could get it pretty accurate with tweaking the computer movement response.
« Last Edit: May 13, 2022, 09:57:26 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #19 on: May 13, 2022, 10:01:14 PM »
Gold mine:
https://app.aircorpslibrary.com/aircraft/link-trainer

An instructor's manual  might actually tell you what the computer response should be to stick movements. I'm guessing the instructor was the computer and controlled the movements?.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #20 on: May 13, 2022, 10:44:20 PM »
Gold mine:
https://app.aircorpslibrary.com/aircraft/link-trainer

An instructor's manual  might actually tell you what the computer response should be to stick movements. I'm guessing the instructor was the computer and controlled the movements?.

Thanks for that, of course the Link Trainer is(was) a clever concoction of bellows, levers, cranks and cams so no conventional computer involved.  The instructor could do things like select wind, turbulence and generally monitor the student pilot executing a simulated instrument flight.  I am sure that manual will make an interesting read none the less.

I have spoken to one of the software gurus and he says we should use SimConnect which he has and is familiar with as it is used in our ATR72 simulator.

Right now I am thinking about hardware!!

John
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Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #21 on: May 13, 2022, 11:26:19 PM »
This is my idea for the "Simulator Simulator"!

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Offline vtsteam

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #22 on: May 14, 2022, 07:47:56 AM »
Okay John, looking forward to what you will do.

One small thing I want to suggest that I experienced with flight sim input devices.....commercial plastic rudder pedals were not realistic in their feel because they could be depressed independently. Real rudder pedals are linked (by the rudder) and so they move opposite each other. If you depress one pedal, the other moves in the opposite direction.

If there are wheel brakes they actuate by toe movement on the top of the rudder pedals. I once made my own rudder pedals linked simply by a cable and small pulleys, all mounted on a small wooden box. It really added a lot to the feel of flying a simulator.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Online John Hill

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #23 on: May 14, 2022, 10:39:42 PM »
Yes, all good stuff.  When I made the pedals for our ATR72 simulator I had a dicken's of a job reducing the number of pivots and levers required to get both pairs to move in a acceptable manner!  Toe brakes and all!

Link simulator will not have too much in the way of brakes etc as the purpose of the Link Trainers was to train pilots to get accustomed to the instruments.

BTW, I see in an opening page of the Link documentation that the Link was deliberately not stable and instructors were advised not to allow students to spend time with the hood open the idea being that they had to learn to use the instruments to control their 'plane.

I had a revelation today when I began to tote up the number of husky steppers etc required for this project so I glanced around for other methods to move the 'plane.   My friendly Chinese purveyor of interesting stuff has pneumatic cylinders for a modest price plus the modern range of click together plumbing make pneumatics rather attractive.  It would also be a use for my stash of washing machine inlet valves.   There are about  3 or 4 air compressors I could choose from to provide the huff.   This would however take me back to square one where I would have to sense the aircraft attitude and somehow integrate that with the FS software.
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Offline PekkaNF

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Re: Electronic stabilization systems. aircraft el al! Link Trainer.
« Reply #24 on: May 16, 2022, 03:39:48 AM »
Looking at those pictures I think that appropriate approach for the cockpit attitude measurement depends on mount to a great extent.

If there are orthogonal bearings (axises) simple absolute position rotary encoders (or even with pulse encoders with "neutral" limit switches) look attractive.

If there is a universal joint, resolving three axises and derivating acceleration out of it becomes challenging.

This friend of mine looked up interweb and found new version of the sensor that is a whole lot more easy to calibrate. This video relates to it, I don't know if that software is available or he just cobled up something for fun....anyway nice to see how responsive the signal is.